1. Field of the Invention
This invention relates to improvements in an image stabilization device for use in an optical instrument such as a camera, which device is carried, for example, on a camera and detects vibration (hand vibration) of a frequency of the order of 1 HZ to 12 HZ and achieves image stabilization with the detected vibration as the information of the image blur state.
2. Related Background Art
The prior art which is the subject of the present invention will hereinafter be described.
In present-day cameras, important operations to photographing such as exposure determination and focusing are all automatized and therefore, the possibility of failing in photographing is very rarely the case even with persons unskilled in the manipulation of cameras, but only the failure in photographing by camera vibration has been difficult to prevent automatically.
So, in recent years, cameras which enable even failure in photographing attributable to such camera vibration to be prevented have been studied very actively and particularly, the development and researches of cameras which can prevent failure in photographing caused by the photographer's hand vibration have been put forward.
The hand vibration of a camera during photographing is usually vibration of a frequency of 1 HZ to 12 Hz, and as a basic idea for enabling a photograph free of image blur to be taken even when such hand vibration is caused at the point of time of shutter release, it is necessary to detect the vibration of the camera caused by the above-mentioned hand vibration, and displace a correction lens in conformity with the detected value. Accordingly, to achieve the above purpose (that is, to enable a photograph free of image blur to be taken even when the vibration of the camera is caused), it becomes necessary to detect the vibration of the camera accurately at first, and correct any variation in the optical axis caused by the hand vibration.
Theoretically speaking, the detection of this vibration (camera vibration) can be accomplished by carrying on a camera a vibration sensor for detecting angular acceleration, angular speed or the like and a camera vibration detecting system for electrically or mechanically integrating the sensor signal and outputting angular displacement. Then, a correcting optical mechanism for making the photographing optical axis eccentric on the basis of the detected information is driven to thereby suppress image blur.
Here, the outline of an image blur suppressing system (image stabilization system) using an angular speed meter will be described with reference to FIG. 22 of the accompanying drawings.
FIG. 22 shows a system for suppressing image vibration resulting from camera's vertical vibration 71p and camera's horizontal vibration 71y in the directions of arrows 71. In FIG. 22, the reference numeral 72 designates a lens barrel, and the reference characters 73p and 73y denote angular speed meters for detecting the camera's vertical vibration angular speed and the camera's horizontal vibration angular speed, respectively, and the angular speed detection directions thereof are indicated by 74p and 74y, respectively. The reference characters 75p and 75y designate conventional analog intergration circuits for integrating the signals of the angular speed meters 73p and 73y, respectively, converting them into hand vibration angular displacements, driving a correcting optical system 76 (77p and 77y denote the driving portions thereof, and 78p and 78y designate correction optical position detecting sensors) by said signals, and securing stability on the image plane 79. The correcting optical mechanism itself may be endowed with a mechanical integrating function and the above-described analog integration circuits may be omitted.
In the system as described above, the angular speed meters 73p and 73y which are vibration detecting means detect the angular speeds of hand vibration, and the outputs thereof must be integrated to find a vibration displacement angle, and the correcting optical system 76 must be driven in conformity therewith.
FIG. 23A of the accompanying drawings shows a board graph of the found integration characteristic, and gain 81 has an integration characteristic (first floor integration characteristic of 20[dB/dec]) from 0.1 HZ or higher.
As previously described, hand vibration is of a frequency of the order of 1 HZ to 12 HZ and therefore, it seems that 1 HZ or higher can be integrated as an integration characteristic, but if as shown in FIG. 23B of the accompanying drawings, a characteristic that 1 HZ or higher is integrated is adopted, phase 84, if not gain 83, is not in a sufficient integration characteristic (a phase delayed by 90 [degrees] with respect to the input angular speed) in the vicinity of 1 HZ, and to attain the target of an image stabilization camera, i.e., to "prevent image vibration from occurring in the use of a 300 mm lens and a 1/8 sec. slow shutter", such a great phase delay hampers accurate image stabilization. Therefore, use is made of the characteristic of FIG. 23A in which the delay of phase 82 in the hand vibration frequency band is small and time constant is great (time constant is greater if the point of bend of the curve of gain 81 in the board graph is more toward the low frequency side).
FIG. 24 of the accompanying drawings diagramatically shows a circuit for making such a characteristic, and a resistor 87 and a capacitor 86 are negatively fed back in parallel to an operational amplifier 85. The greater the resistance value of the resistor 87 and the capacity of the capacitor 86 are made greater becomes the above-mentioned time constant.
When in FIG. 24, the signal of an angular speed meter is input to a terminal 88, a vibration displacement angle is output from a terminal 89, and as shown by the phase 82 of FIG. 23A, the accuracy of a vibration angle of 1 HZ or higher is ensured, but when use is made of a circuit having such a great time constant, the following problem arises.
The time constant being great means that a long time is required until the output becomes stable. For example, when the point of bend in FIG. 23A is at 0.1 HZ, the time constant is 1.59, and two seconds is required until the output is stabilized to some extent.
This will be graphically shown. In FIG. 25 of the accompanying drawings, relative to the center 810a of hand vibration 810 shown by a sine wave, the angular speed meter detects a hand vibration angular speed from arrow 811, and the center 812a of a waveform 812 obtained by integrating the output of the angular speed meter by an integration circuit of time constant 1.59 to find hand vibration has an error of low frequency superposed thereon. This is the error until the stabilization of the output, and if photographing is effected (from the point of time of arrow 813) when this error is arising, the amount indicated by hatching 814 within exposure time will remain as image vibration.
Accordingly, in the case of such an image stabilization system, there has been the possibility of inviting the failure that photographing is effected before the stabilization of the output and a photograph in which vibration is not corrected is taken.